I have a personal policy of never using the word ki. Nobody seems to be able to agree on what it means, and I don't think there's anything in the martial arts that is too mysterious to be explained with words that have agreed-upon definitions. There are a lot of other aikido people who would be very offended to hear me say that, though.

some karate-teacher (don't remember the name, he was JKA, from Hawaii, around the year 2000 at a seminar in Hamburg. Most likely 3rd Dan or higher) let us practice some basic over-the-shoulder-throw. After that, he told us to force our ki to our feet - thus we would be much harder to throw, because the ki would hold us to the ground. Because we would weigh more.

Therefore, ki is spacetime-distortion.

Therefore, fat people have more ki.

Also he shared some of his wisdom with us - "you can make small mistakes in life, but do not do big mistakes".

It's a means of describing a concept. If you punch me in the gut and make me puke/lose the fight, and you believe it was chi, then I can't disagree with you, because you did exactly what you wanted to. If building/developing/controlling/channeling the chi is how you believe you get strong, and it works, then nobody can say anything else.